On January 7, 1985, Japan launched a spacecraft originally known as MS-T5
which was then renamed to Sakigake (Japanese word for "Pioneer").
Sakigake was Japan's first ever deep space probe and its mission was to
measure the solar wind and magnetic field as it flew by Halley's Comet.
Sakigake was identical to its twin, Suisei, except for its instrument payload.
Sakigake carried no imaging instruments. On March 11, 1986, Sakigake
made its closest approach to Halley's Comet at a distance of 6.99 million km.
Sakigake discovered that the solar wind was affected by the comet's
presence at the 6.99 million km distance, but this result conflicted with Suisei's measurement
of 420,000 km. Shortly after its closest approach, Sakigake served as
a reference spacecraft for Giotto's encounter which helped eliminate
Earth atmospheric interference with Giotto's radio signals.

Suisei was Japan's second deep space mission to study Comet Halley. Suisei, meaning "Comet" in
Japanese, was identical to Sakigake except for its instrument load. Launched on
August 18, 1985, Suisei began observation of Comet Halley in November 1985.
The spacecraft returned up to six UV images a day of the comet. Just prior
to its closest approach on March 8, 1986, the UV instrument was switched off
and the the solar wind experiment was turned on. Cometary water, carbon
monoxide and carbon dioxide ions were detected. During closest approach,
Suisei was hit by two dust particles which slightly changed the spin axis and
spin period of the spacecraft. After the encounter, Suisei continued to
monitor Comet Halley, and detected two major and four minor outbursts from
the comet as it rotated.

Sakigake is still active and is expected to survive well into the
1990's. Since the Halley's Comet flyby, Sakigake has made a number of
Earth
flybys with the last occuring on July 3, 1995. However, almost no fuel remains
after the last flyby, and it is now no longer possible to send Sakigake to comet
Giacobini-Zinner in 1998.

Suisei was planned for a comet Giacobini-Zinner encouter in November 1998.
However, the mission ended when Suisei ran out of propellant on February 22, 1991.
The spacecraft shut itself off and hasn't been heard from since.